Chemical Physics Letters vol:439 issue:1-3 pages:213-218
The UV/visible and CD spectra of bridged triarylamine helicenes have been simulated using the TDDFT/B3LYP/6-31+G(d) method. They reproduce well the experimental spectra. For M-helicenes, the Cotton effect associated with the lowest-energy transition is negative for the smallest helicenes and becomes positive for the largest one, as a result of the variations of the angle between the electric and magnetic transition dipole moments. Since these species are stable upon oxidation, the UV/visible and CD spectra of their radical cations have been simulated. They show low-energy absorption and CD bands, figuring out enhancement of the first hyperpolarizability. (C) 2007 Elsevier B.V. All rights reserved.